Some of what you say it true, but leaves out this important fact
A big bet on a single horse crushes that horses odds, but does relatively little for the others on the upside, since it's distributed evenly among the whole field. .
So when the whale horse wins , you get ripped, but when it loses, you win only modestly more.
Your edge would come by avoiding the whale horse altogether, though that's easier said than done, and would require you to pass many races
